This invention relates to high selectivity microporous UZM-5 zeolite membranes. In addition, the invention relates to methods of making and using these microporous UZM-5 zeolite membranes.
Gas separation processes with membranes have undergone a major evolution since the introduction of the first membrane-based industrial hydrogen separation process about two decades ago. The design of new materials and more efficient methods continue to advance membrane gas separation processes.
The gas transport properties of many glassy and rubbery polymers have been measured as part of the search for materials with high permeability and high selectivity for potential use as gas separation membranes. Unfortunately, an important limitation in the development of new membranes for gas separation applications is a well-known trade-off between permeability and selectivity of polymers. By comparing the data of hundreds of different polymers, Robeson demonstrated that selectivity and permeability seem to be inseparably linked to one another, in a relation where selectivity increases as permeability decreases and vice versa.
Despite concentrated efforts to tailor polymer structure to improve the separation properties of polymer membranes, current polymeric membrane materials have seemingly reached a limit in the trade-off between productivity and selectivity. For example, many polyimide and polyetherimide glassy polymers such as Ultem® 1000 have much higher intrinsic CO2/CH4 selectivities (αCO2/CH4) (˜30 at 50° C. and 791 kPa (100 psig) pure gas tests) than cellulose acetate (˜22), which are more attractive for practical gas separation applications. These polyimide and polyetherimide glassy polymers, however, do not have outstanding permeabilities attractive for commercialization compared to current commercial cellulose acetate membrane products, consistent with the trade-off relationship reported by Robeson. In addition, gas separation processes based on glassy polymer membranes frequently suffer from plasticization of the stiff polymer matrix by sorbed penetrant molecules such as CO2 or C3H6. Plasticization of the polymer is represented by membrane structure swelling and a significant increase in the permeabilities of all components in the feed and occurs above the plasticization pressure when the feed gas mixture contains condensable gases. Plasticization therefore decreases the selectivity of the membrane.
On the other hand, inorganic microporous molecular sieve membranes such as zeolite membranes have the potential for separation of gases under conditions where polymeric membranes cannot be used, thus taking advantage of the superior thermal and chemical stability, good erosion resistance, and high plasticization resistance to condensable gases of the zeolite membranes.
Microporous molecular sieves are inorganic microporous crystalline materials with pores of a well-defined size ranging from about 0.2 to 2 nm. Zeolites are crystalline aluminosilicate compositions which are microporous and which have a three-dimensional oxide framework formed from corner sharing AlO2 and SiO2 tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared are used in various industrial processes. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure.
Non-zeolitic molecular sieves are based on other compositions such as aluminophosphate, silicoaluminophosphate, and silica. Representative examples of microporous molecular sieves are small-pore molecular sieves such as SAPO-34, Si-DDR, UZM-9, AlPO-14, AlPO-34, AlPO-17, SSZ-62, SSZ-13, AlPO-18, LTA, UZM-13, ERS-12, CDS-1, MCM-65, MCM-47, 4A, 5A, UZM-5, SAPO-44, SAPO-47, SAPO-17, CVX-7, SAPO-35, SAPO-56, AlPO-52, SAPO-43, medium-pore molecular sieves such as Si-MFI, Si-BEA, Si-MEL, an large-pore molecular sieves such as FAU, OFF, zeolite L, NaX, NaY, and CaY. Membranes made from some of these microporous molecular sieve materials provide separation properties mainly based on molecular sieving or a competitive adsorption mechanism. Separation with microporous molecular sieve membranes is mainly based on competitive adsorption when the pores of large- and medium-pore microporous molecular sieves are much larger than the molecules to be separated. Separation with microporous molecular sieve membranes is mainly based on molecular sieving or both molecular sieving and competitive adsorption when the pores of small-pore microporous molecular sieves are smaller or similar to one molecule but are larger than other molecules in a mixture to be separated.
A majority of inorganic microporous molecular sieve membranes supported on a porous membrane support reported to date are composed of MFI. The pores of MFI zeolites are approximately 0.5-0.6 nm, and are larger than CO2, CH4, and N2. Lovallo et al. obtained a selectivity of about 10 for CO2/CH4 separation using a high-silica MFI membrane at 393° K (see Lovallo et al., AICHE JOURNAL, 1998, 44, 1903). The pores of FAU zeolite are approximately 0.78 nm in size, and are larger than the molecular sizes of H2 and N2. High separation factors have been reported for CO2/N2 mixtures using FAU-type zeolite membranes (see Kusakabe et al., INDUSTRIAL ENGINEERING CHEMICAL RESEARCH, 1997, 36, 649; Kusakabe et al., AICHE JOURNAL, 1999, 45, 1220). Permeation and adsorption experiments indicate that the high separation factors can be explained by competitive adsorption of CO2 and N2.
In recent years, some small-pore microporous molecular sieve membranes such as zeolite T (0.41 nm pore diameter), DDR (0.36×0.44 nm), and SAPO-34 (0.38 nm) have been prepared. These membranes possess pores that are similar in size to CH4, but larger than CO2 and have high CO2/CH4 selectivities due to a combination of differences in diffusivity and competitive adsorption.
Since the discovery of a series of UOP Zeolite Materials (UZMs) by Lewis et al. in most recent years, these materials have been used in catalysis, separation, and as advanced functional materials. See Lewis et al., Angew. CHEM. INT. ED., 2003, 42, 1737; WO2002036489 A1; W02002036491 A1; W02003068679 A1; US 6,756,030; US 2005/065016 A1; U.S. Pat. No. 7,578,993. UZM zeolite materials are a family of aluminosilicate and pure silica zeolite materials with unique framework type structure, uniform pore size, and unique properties such as ion-exchange property synthesized by a Charge Density Mismatch method. The family of zeolites that are designated as UZM-5 have now been found to have particular utility in zeolite membranes.
UZM-5 zeolites are a family of zeolites which are described in U.S. Pat. No. 6,613,302, U.S. Pat. No. 6,388,159, and U.S. Pat. No. 7,578,993, which are incorporated by reference in their entirety. The UZM-5 zeolitic compositions have a unique x-ray diffraction pattern and have an empirical formula on an anhydrous basis in terms of molar ratios of:Mmn+Rrp+Al(1-x)ExSiyOz where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, m is the mole ratio of M to (Al+E) and varies from about 0 to about 1.2, R is a nitrogen-containing organic cation selected from the group consisting of quaternary ammonium ions, protonated amines, protonated diamines, protonated alkanolamines, quaternary alkanolammonium ions, diquaternary ammonium ions, and mixtures thereof, r is the mole ratio of R to (Al+E) and has a value of about 0.25 to about 3.0, E is an element selected from the group consisting of Ga, Fe, and B, x is the mole fraction of E and varies from 0 to about 0.5, n is the weighted average valence of M and has a value of +1 to about +2, p is the weighted average valence of R and has a value of +1 to about +2, y is the mole ratio of Si to (Al+E) and varies from about 5 to about 12, and z is the mole ratio of O to Al and has a value determined by the equation:z=(m•n+r•p+3+4•y)/2the zeolite is characterized in that it has at least two x-ray diffraction peaks, one at a d-spacing of 3.84±0.07 Å and one at a d-spacing of 8.55±0.25 Å.
The above-described UZM-5 zeolites are prepared by forming a reaction mixture (or called UZM-5 zeolite-forming gel) containing reactive sources of R, Al, Si and optionally E and/or M and heating the reaction mixture (or called UZM-5 zeolite-forming gel) at a temperature of about 100° to about 175° C., the reaction mixture having a composition expressed in terms of mole ratios of the oxides of:aM2/nO:bR2/pO:(1−c)Al2O3:cE2O3:dSiO2:eH2Owhere “a” has a value of about 0 to about 2.0, “b” has a value of about 1.5 to about 30, “c” has a value of about 0 to about 0.5, “d” has a value of 5 to about 30, and “e” has a value of about 30 to about 6000.
Further details regarding the preparation of UZM-5 materials may be found in U.S. Pat. No. 6,613,302 and U.S. Pat. No. 6,982,074 incorporated by reference herein in their entireties.
The present invention involves novel UZM-5 zeolite membranes comprising UZM-5, methods for making the same, and methods of separating gases, vapors, and liquids by using these UZM-5 zeolite membranes. Specific members of this family of zeolites are UZM-5, UZM-5P and UZM-5HS.
These membranes offer several advantages over polymeric membranes, including high selectivity due to their uniform pore size, superior thermal and chemical stability, good erosion resistance, and high CO2 plasticization resistance for gas, vapor, and liquid separations.